1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image in an electronic photographing process using a laser printer, etc.
2. Description of the Related Art
Generally, image forming apparatuses include an electronic photographic process unit which performs the steps of charging, exposure, development, transfer, peeling, cleaning, and the like. An image is transferred on a paper sheet by passing the sheet through the image transfer section of the process unit, and is fixed to the sheet by passing the sheet between a pair of fixing rollers.
This type of conventional image forming apparatus employs a cartridge type developer ("toner") supply container for supplying toner to a developing device built in the apparatus body, as disclosed in U.S. Pat. No. 5,017,966, for example. The supply container is removably fitted to the apparatus body and detachably connected to the developing device.
Untransferred toner, which has not been transferred on the paper sheet at the image transfer section, is removed from a photoconductive body by a cleaning device. The removed toner is brought to the outside of the process unit and is collected in a cartridge type recovery container. The recovery container is also detachably fitted to the process unit.
When the "empty" state of the toner supply container and the "full" state of the recovery container are detected by a detector, the operator exchanges the containers on the basis of the detection result.
In conventional apparatuses, the toner supply container and the toner recovery container are separated, or, in order to simplify the exchange process, the containers are integrated with the process unit, as disclosed in U.S. Pat. No. 4,771,313.
In the former case, however, the containers must be independently exchanged each time the toner is supplied or the used toner is dumped. This is troublesome.
In the latter case, the exchange operation can be simplified; however, the storage amounts of supply toner and used toner are limited, owing to the practical size of the integrated process unit. Consequently, the exchange cycle of the entire unit is shortened, and the unit must be exchanged earlier than the end of the lifetime of the relatively expensive developing device, cleaning device and photoconductive drum. Thus, the running cost of the apparatus increases.